Israel attempts first boots-on-the ground operation as 22 members of same family killed in air strike

Israeli naval commandos fought Hamas gunmen in a dramatic beach front firefight on Sunday after Israel attempted the first boots-on-the ground operation of its ongoing offensive in Gaza.

Benjamin Netanyahu, the Israeli prime minister, later warned that the military operation, that has so far killed 166 Palestinians, could gone on for a "long time".

The early morning clash broke out after Hamas militants – alerted by a lookout stationed in a nearby mosque – intercepted Israeli special forces trying wade ashore at Sudaniya in northern Gaza.

The two sides engaged each other in the sea, according to one witness account, in two hours of shooting that left four Israeli troops wounded. The Israeli military said the mission had achieved its goal of destroying rocket launching sites near the beach.

The amphibious landing came after as Israeli reservists massed along the Gaza land frontier with tanks and artillery fire for a possible ground invasion following six days of aerial bombardment.

Sa'ad Dowla, a caretaker at the al-Mathaf Hotel, less than 100 yards from the scene of the Sunday's firefight said he heard Palestinian shooting first. "When I looked out, both sides were in the sea shooting at each other," he said. "After the shooting started, an Israeli helicopter came and started strafing the water."

The fight happened after an Israeli bomb attack killed up to 22 members of the same family in a targeted strike on the home of Gaza's Hamas police chief. It was biggest death toll recorded in a single strike since Israel began Operation Protective Edge last Tuesday.

Tayseer Batsh, the police chief, was critically injured in Saturday night's incident, which happened at 10pm, about an hour after Hamas launched a choreographed fusillade of rockets aimed at Tel Aviv.

Eyewitnesses described two large bombs striking the Batsh family home in Gaza City's Tuffah neighbourhood, setting off an ear-splitting explosion and filling the air with smoke and dust.

A gaping deep crater was left where the house had stood.

"The explosions were like an earthquake. We could feel the ground shaking under us," said Mohammed Batsh, a family relative and civil engineering student who was returning from a nearby mosque at the time.

"The smoke was so thick that we couldn't see for at least 15 minutes. After it cleared, I saw body parts everywhere, some of them thrown a long way away. I know all the people in that house but the corpses were so badly torn to pieces that I didn't recognise them.

Palestinian mourners carry the body of a member of the Al-Batsh family who was killed during the Israeli airstrike (Hatem Moussa/AP)

"The majority of the people killed were civilians. They were not involved in military activities."

Seventeen members of the extended family were confirmed dead while earth-moving machines searched on Sunday for another five missing, presumed dead, including a pregnant woman. A badly charred severed arm was found in the grounds of a nearby school, prompting shouts of "there is no God but Allah" from onlookers.

As the death toll rose, residents fled the northern Gaza town of Beit Lahiya in a mass exodus prompted by a warning from the Israeli army in dropped leaflets and text messages that they should evacuate their homes by 12 noon local time to avoid the consequences of a planned bombardment.

Around 4,000 people – many carrying bedding and other possessions on donkey carts – crowded into eight UN schools specially opened to accommodate them.

The reverberating sound of explosions could be heard from inside Beit Lahiya's local hospital after the evacuation deadline.

A member of the Al-Batsh family, who were killed in an Israeli air strike, mourns during their funeral (Mohammed Salem/Reuters)

Amid intensifying international pressure for a ceasefire, Hamas continued to fire rockets into Israel on Sunday – bring the number of missiles launched by the Islamist group in the past week to more than 830, the Israeli army said. There have been no Israeli fatalities.

Benjamin Netanyahu, the Israeli prime minister, said Hamas was to blame for all civilian casualties in Gaza and that the "patient and level-headed" action against militants would continue.

Laurent Fabius, the French foreign minister – speaking in Vienna at a gathering of six world powers, including Britain, being held to negotiate with Iran over its nuclear programme, said a ceasefire was "an absolute priority".

John Kerry, the US secretary of state, spoke to Mr Netanyahu on Sunday to renew a US offer to help mediate a truce. He "highlighted the US concern about escalating tensions on the ground," a senior State Department official said.

Speaking late on Sunday night, UN chief Ban Ki-moon said "too many" Palestinian civilians had been killed, and urged Israel to scrap plans for a potentially devastating ground offensive.

The secretary-general said he "feels a sense of responsibility for the Palestinians who, especially in the Gaza Strip, have long been denied the sense of freedom and dignity that they deserve."

Reiterating his condemnation of the firing of rockets into Israel by the Islamist movement Hamas that rules Gaza, Mr Ban demanded an "immediate cessation of these indecent attacks."

But a "deeply worried" UN chief also stressed that "too many Palestinian civilians have been killed, and any Israeli ground offensive will undoubtedly increase the death toll and exacerbate civilian suffering in the Gaza Strip."